Method of making oil hole drills



Feb. 28, 1939.

s. A. coesDuu.

METHOD OF MAKING OIL- HOLE DRILLS Fild May 9,1938 I 3 Sheets-Sheet 1 11vVENTOR 5Zzz4r'Z 62554 222: BY

I Y A TTORNEI Feb. 28, 1939.

S. A. COGSDILL METHOD OF MAKING OIL HOLE DRILLS Filed May' 9, 1938 3Sheets-Sheet 2 INVENTOR jie'iydrz f2 d'dgsd'z'll B Y I I I A T T ORNEY5.

Patented Feb. 28, 1939 UNlTED STATES" mrrnon or PATENT OFFICE MAKING OILHOLE Application May 9, 1938, Serial No. 206,865

2 Claims.

This invention relates to oil hole drills and particularly to a methodof making the same, the principal object being the provision of suchmethod by the practice of which oil holedrills of superiorcharacteristics may be. manufactured in an economical manner.

Objects of the invention include the provision of a method of making anoil hole drill in which the b nk may be formed with spiral flutesprevlous to the step of providing the oil holes therein; a method ofmaking an oil hole drill eliminatlng the necessity of rifle drilling; amethod of making an oil hole drill in which the oil holes in an initialstage of operation are formed by milling or otherwise providing a grooveopening onto the exterior surface of the drill blank in parallelrelation with respect to the usual flutes; a meth- 0d of making an oilhole drill including the steps of forming a groove in a drill blank andthereafter working the metal of the blank at and ad- I jacentthe'periphery thereof into the outer portions of the groove to cl'oseit, thereby providing an oil hole within the blank; and a method offorming an oil hole drill including the steps-of spirally fluting ablank, providing one or more grooves opening onto the exterior surfaceof the blank and extending in approximate parallelism with respect to amarginal edge of at least one of the flutes, and then acting upon theblank to work the metal thereof at and adjacent the exterior surfacethereof into the outer portion trate suitable examples of oil holedrills formed in accordance with the present invention, illustratingvarious steps in the operation of forming the drills and suitableapparatus for use in forming the same, I

Fig. 1 is a partially broken side elevational view of an oil hole drillof the type having a cylindrical or straight shank;

Fig. 2 is a fragmentary partially broken side elevational view of an oilhole drill having a tapered shank;

Fig. 3 is a transverse sectional view taken throughthe fluted portion ofa blank'suoh-as is provided in accordance with'the present invention inthe formation of drills such as illustrated in Figs. -1 and 2; Fi 4 is aview similar to Fig. 3 but illustrating a subsequent step of operationin the forming of the drill;

Fig.- 5 is a fragmentary side elevational view of a drill lank after theoperation illustrated in- Fig. 4-has been completed;

- Fig. 6 is a more or less diagrammatic view taken transversely througha drill blank such as iilusl0 trated in Fig. 5 and illustrating asubsequent step of operation thereon in which the metal of the blank iscausedto close the outer edges of the grooves formed by the operationillustrated in Fig. 4 thereby to form oil holes in the drill;

Fig. 7 is a transverse sectional view through a completed drill formedin. accordance with the present invention 'and constitutes a slightlyenlarged transverse sectional view taken through the fluted portion ofthe drill shown in Figs. 1 or 2;

Fig. 8 is a fragmentary side elevational view of an oil hole drillarranged for side feeding of liquid into the oil holes thereof;

Fig; 9 is an end elevational view, partly in section, of an apparatus bymeans ofwhich the operation illustrated in Fig. 6 may be suitablyaccomplished; I

Fig. 10 is a partially broken plan view of the apparatus shown in Fi 9;

Fig. 11 isa side elevational view of the appsratus shown in Figs'. 9 and10, certain parts thereof being broken away to better illustrate theconstruction and parts being shown in section.

Drills of the type employed for cutting metal I and having one or morepassages therethrough for conveying a stream of liquid to the point ofthe drill are. commonly known as oil hole drills although in manycases'liquid which is actually caused to flow through the drill does notconsist 4o of oil. In the majority of cases, however, theliquid actuallyused will serve as a lubricant for the drill even though the lubricantconsists of water, either plain or with the addition of soda,

, as is commonly employed in cutting steels, 4s

-- wrought and malleable iron, aluminum and other soft alloys, or it maybe other aqueous drilling compounds such as are commonly; sold on themarket. Such liquid has an additionally imporl tant function in more orless heavy production so drilling, namely that of a coolant, it thusserving to cool the cutting edge of the drill and prevent it frombecoming over-heated, thus permitting the. v drill to maintain itsproper cutting edge for a greater length of time than would otherwisebeu 35 thereof desired'in the final product.

possible. Particularly in drilling relatively deep holes the flow ofsuch liquid through a drill has an additional important function ofserving to carry away the chips out of the drill opening, thuspreventing the chips from packing up in the hole and endangeringbreakage of the drill, as Well as eliminating the necessity ofrepeatedly removing the drill from the opening to clear the drill andopening of chips during the drilling opelation.

It will be understood that oil hole drills are usually identical insubstantially all respects to ordinary drills except for the provisionof the oil hole or holes therein. In other words they are usually of thespirally fluted type having two or more spirally arranged flutes andcorresponding lands and usually provided with the conventional ,bodyclearance back of the margin or cutting edge thereof. The drills may beof the conventional or so-called straight shank type or of theconventional taper shank type. While the present invention is applicableto such drills regardless of the number of flutes provided therein, forthe purpose of simplicity in illustration and description drills of thetwo flute type only will be referred to, the application of the presentinvention to drills having a greater number 91' flutes being readilyapparent to those skilled in the art upon the disclosure herein. a

The conventional method of forming oil hole drills is to form a drillblank with a pair of opposed flutes in opposite sides thereof but withthe flutes straight and parallel to the axis of the blank asdlfierentiated from the spiral conformation The drill blank with thesestraight flutes in it is then rifle drilled from one end thereof to theother end thereof to provide the oil holes, these holes, because of thestraight conformation of the flutes in the blank at this stage ofoperation, thus being arranged in parallel relation with respect to theflutes. After the oil holes are drilled the fluted end of the blank isthen twisted so as to impart to the flute the desired helix angle.Drills constructed in accordance with this practice are necessarilyrelatively expensive to produce because of the'time and labor involvedin drilling the elongated oil holes in the blank, the relatively highpercentage of breakage of the drills employed in drilling the oil holes,the labor and care required in twisting the drill blank into the desiredspiral conformation, and for other reasons well understood to thoseskilled in the art.

Another type of oil hole drill construction has been suggested and inwhich the drill blank is initially spirally fluted in the usual mannerand then a groove is milled or otherwise formed in each land of thedrill spirally thereof in parallel relation with respect to the lands, asmall tube is then disposed in the bottom of each of the grooves and theremaining portion of the groove is filled in usually with a brazingmaterial until that part of the groove not occupied by the tube iscompletely filled with such material. The drill blank reaching suchcondition may then be machined in a conventional way to bring it tocompleted condition. This last typeof oil hole drill has not provencommercially satisfactory for the reason that by its use the torsionalstrength of the drill is considerably reduced and the chips formedduring the drilling operation in working around the drill tend to stickin the brazingmaterial exposed on the surface of the drill at the outerend of the groove and thus pack together, endangering breakage of thedrill, and the brazing material also tends to tear out in part, leavinga rough surface restricting escape of the chips and further tending tocause the same to packaround the drill.

In both of the conventional methods above described it is substantiallyimpossible or at least commercially impractical to employ them in theproduction of oil hole drills smaller than 2; of an inch in diameter,particularly where the drills are of such length as compared to theirdiameter as to come within the classification of long drills. The reasonis that in drills produced by the first method it requires a relativelylong hole to be drilled by a relatively small diameter drill making itsubstantially impossible to prevent run out of the drill and involving alarge number of breakages of the drills employed for drilling the oilholes. the slot required for reception of the oil hole tube makes italtogether impossible to employ the method on smaller drills and onthose slightly larger reduces the torsional strength of the drill tosuch an extent as to render them unsuitable for use.

Drills made in accordance with the present invention may be produced ata materially smaller cost than in either of the two methods previouslydescribed; the present invention is applicable to the manufacture of oilhole drills of a diameter materially smaller than possible in accordancewith previous practices, and this regardless of length; and testsindicate that the resulting drillv itself is of greater strengthtorsionally than drills constructed in accordance with previouspractices. i

In accordance with the present invention the drill blank is providedwith the flutes desired in the finished drill and which fiuteswill, ofcourse, usually be spirally arranged around the axis of the drill. Oneor more relatively deep grooves are provided in the outer peripheralsurface or lands of the drill blank, preferably in the same spiralrelation as the flutes therein and preferably in parallel relation to amarginal edge of the corresponding flute. These grooves and the flutesmay be formed simultaneously with each other or either one prior to theother. The grooves thus formed thus correspond in a measure to thegrooves formed in the drill blank according to the second conventionalmethod above described and which insuch conventional method is adaptedto receive a tube which will later serve as an oil hole. In the broaderaspects of the present invention the groove or grooves thus formed inaccordance with the present invention in'the drill blank may also serveto receive such a tube. but inasmuch as its use would be more or lesssuperfluous and is not required for the practice of the presentinvention it will ordinarily not be employed. Regardless of whether ornot such tube is employed the. blank thus fluted and grooved issubjected to a suitable operation whereby metal of the drill blank atand adjacent the lands thereof is caused to flow or otherwise bedisplaced towards the center of the groove or grooves adjacent theperiphery of the blank and so as to completely close the outer edges ofsuch grooves without causing the bottom portions of the grooves to belikewise closed. As will be apparent by this operation the grooves areautomatically formed into peripherally walled openings open only at theopposite ends of the drill blank, thus provid ng the oil holes desiredin the finished product. the metal at the surface of the lands into theThe operation of displacing- In the second method the relative size ofopen edges or tops of the grooves may be employed for simultaneouslyforming part or all of the usual body clearance provided in suchv drillsback of the cutting edges or margins, this metal flowing or displacingsteps thus serving a dual purpose. Once the open edges of the grooveshave been closed the drill blank may be completed in accordance withconventional practice.

It may be mentioned that while the step of closing the open edges of thegrooves as above described in accordance with the present invention inthe broader aspects of the invention may be accomplished in any suitablemanner as for instance by peening, swaging or the like, it is preferablyaccomplished by a suitable rolling operation and-by the use of which thesurface layer of metal over part or all of the body clearance area ofthe drill is compacted and densified. This 'densiflcation of thissurface portion of the drill tices of the present invention in thisrespect has a greater resistance to breaking under torsional strainsthan ordinary types of drillsnot provided with oil holes and constructedfrom the same material. The present invention, however, is not concernedwith the drill itself as an article, but

only to the method of manufacturing the same.

Referring to the drawings and particularly to Fig. 1 a drill is showncomprising a body indicated generally at 20 and a shank 22, the shank 22inthis case being a so-called straight or cylindrical shank. The body 20is provided with a pair of diametrically opposite conventional flutes24'arranged spirally of the axis of the drill, there being acorresponding number of lands 26 separating. the flutes 24. The lands 26are each provided with a cutting edge or margin 28 along holes 20a.

that edge thereof more advanced in the intended direction of rotationand the remainder of the lands are radially inwardly relieved withrespect to such margin or cutting edge to provide the usual bodyclearance. That portion of the body 2001' the drill between the flute 24and below each land 26 is provided with a so-called oil hole'30, the oilholes 30 extending from the point 32 of the drill in the same" spiralrelation as the flutes 24 into the shank 22 where they open intoenlarged centrally arranged openings or pockets 34 provided therein. Itwill, of course, be understood that in actual practice the chuck orother fixture which receives and supports the shank 22 of the drill isprovided with suitable means for applying a suitable liquid to theinterior of the opening 34 from which it will flow through the oil holes30 to the point32 of the drill forthe purposes above described.

v A modified-arrangement for introducing liquid The drill illustratedin.Fig. 21s substantially identical to the drill illustrated in Fig. 1except for' the shank portion thereof. Accordingly, like numeralsillustrate like parts except that such ance with conventional practice.

numerals bear a prime mark. The shank 22' in this case instead of beingcylindrical is tapered or formed as the frustur'n of a cone and itsextreme'end is provided with a tang 36 in accord- The oil'holes 30 inthis case instead of opening into an enlarged opening or pocket in theshank .22 are each connected adjacent the junction of the main body 20with the shank 22' with a corresponding straight opening 38 extending inaxially parallel relation through the length of the shank 22' andopening on the outer end of the tang 36. As will hereinafter be obviousit makes no difference what type of shank is provided on a drillorwhatmethod is followed in supplying liquid to the oil holes in thedrill in accordance with the present invention, but for the purpose ofease in description only, unless otherwise specified, it willhereinafter be considered that the type of drill shown inFlg. l is theone referred to in the following description.

As previously mentioned it makes no difference in accordance with .thebroader aspects of the present invention whether or not the flutes andgrooves. are formed simultaneously with each other, whether the flutesare formed previouslyto the grooves, or whether the grooves are formedpreviously to the flutes and this fact is to be kept in mind, inthefollowing description and claims even though, for'the reason ofsimplicity in description, it will be assumed that the flutes are formedfirst and thegrooves afterwards.

In making the drill shown inFig. 1 a suitable length of cylindricalstock is first prepared, corresponding in length and diameter to thedesired finished drill. In such cases this piece of stock may comprise,for instance, a body portion corresponding to the body portion 26 ofhigh speed steel and a shank portion corresponding to. the

shank 22 of low carbon or other suitable steel.

vention the flutes 24 may be first formed straight, .and likewise thegrooves, and that the body of the drill later twisted to the desiredspiral, but inasmuch as this would involve an additional and unnecessarystep it will be assumed that the flutes 24 will be formed in the blankin the same spiral relation as desired in the finished product by anysuitable or conventional method as, for instance, by a millingoperation. In such case after the flutes 24 are formed in the blank thecross-sec-.

tlonal conformation of the'body portionof the blank will he thatillustrated in Fig. 3.

The next operation is to. form one or more grooves 4|! in the blank andwhich may be accomplished in any suitable manner as, for in-' imatelyequal to half the radius of the blank.

The bottom of the grooves 40 are preferably rounded or'of semi-circularconformation and the width of the grooves 40 equal to the diameter ofthe oil hole desired in the ultimate product particularly where, as isdesirable, no separate oil hole tube is to be employed. As illustratedin Flg. 5 the grooves 40 extend from the point 32 into that end of theshank 22 which joins the body 26 and, being centrally located withrespect to their corresponding lands 2B are, accordingly, arranged inspiral formation in approximate par allelism with the adjacent marginsof the flutes 24. 1

The next operation consists in working the metal adjacent the surface ofthe lands 26 into the outer edges ofthe grooves 40 so as to completelyclose such outer edges while still leaving the inner or bottom portionsof the grooves 411 open thereby to provide oil holes. If for any reasonwhatever it is desired to employ oil hole tubes, it will be understoodthat these tubes would be positioned in the bottoms of the grooves 40previous to the operation of closing the outer edges of the groovesdisclosed in Fig. 6.

In the broader aspects of the present invention the metal at andadjacent the surface of the lands 26 may be worked inwardly towards thecorresponding grooves 40 to close the outer edges thereof in any desiredmanner as long as the operation effects the purpose of closing the outeredges of the grooves. The working or flowing of the surface metal-of thelands 26 to close the grooves is preferably accomplished by a rollingoperation as illustrated in Fig. 6. In carrying out this operation apair of rollers 42, each peripherally shaped to accurately fit one ofthe grooves 24, are engaged in the grooves 24 and are pressed firmlytoward one another therein. The purpose of the rollers 42 is twofold inthat they not only serve to guide and turn the blank in its passagetherethiough but also, where located sufficiently 'close to the metaldisplacing rollers aid in preventing displacement of the metal of theblank into the flutes 24 during the rolling operation. A second pair ofrollers 44 are provided in alternate relation with respect to therollers 42. The rollers 44 are each provided with a concave sectionedperipheral portion 46 of a curvature preferably corresponding with thecurvature of that portion of the final product providing the bodyclearance back of the cutting edge or margin 26, and bevel side faces48. Means are provided. for urging the rollers 44 toward one another.

It will be appreciated that when the rollers 44 are'flrst brought intoengagement with the lands 26, they will bear against the correspondinglands 26 only at the junction of the curved faces '46 with the bevelfaces 48, this being because of the fact that under such circumstancesthe radius ofthe faces 46 will be less than the radius of the outsidediameter of the blank. Accordingly, when pressure is applied to therollers urging them toward one another there will be a tendency for themetal between the outer margins of the curved faces 46 to be crowdedcentrally inwardly and because the rollers 44 are arranged centrally oftheir corresponding grooves 40, to crown such metal into the open outeredges of the grooves toclose the same. With suitablepressurethusl'applied to the rollers 44 the blank is drawn between ers42 and 44 until the rollers 44 have been imbedded in its surface asufficient extent to completely close the outer ends of the grooves andthereby provide the oil holes .30 therein as well as to provide asuitable amount of body clearance over the width of the rolls 44.

After the operation disclosed in Fig. 6 is completed the drill blank isremoved from between the rollers 42 and 44, the opening 34 may bemachined in the shank 22 and suitable holes drilled through its bottomend to connect the interior thereof with the oil holes 30, and whereonly one margin 28 on each land 26 is desired and as ordinarily will bethe case in connection with the drills for drilling metal, theprojecting portion of the land at its trailing edge may be removed asindicated in Fig; '7, and the drill hardened, ground or otherwise actedupon to bring it to its final con dition.

It will, of course, be understood that where the form of constructionshown in Fig. 8 is desired, the rolling operation disclosed inconnection with Fig 6 will close the grooves 40 over all their lengthexcept that small end portion thereof in the shank which is adapted tolater form the inlet openings 35, and in such case no subsequent op--eration of drilling through the free end of the shank to providecommunication with the correspondingends of the openings 30a isrequired.

It may be stated at this point that where the operation disclosed ,inFig. 6 is properly carried out, the metal which is displaced over theopen ends of the'grooves 4b to form the openings all is so densified andcompacted, as will be appreciated by those-skilled in the art, as toimpart a materially added stiffness to this portion of the drill. Thisis particularly true where this metal is worked cold, in other wordswhere no artificial heating of the drill blank is resorted to during theoperation disclosed in Fig. 6, and tests have shown that under suchconditions the resistance of the drill to breakage under torsionalstrains is smaller drills, it may be found necessary to preheat thedrill blanks before the operation described in Fig. 6 is carried out soas to enable a proper flow of the metal over the open end of the groovesto be obtained. The temperatures to which the blank is heated in suchcase is preferably approximately those temperatures to which thematerial from which the drill body is made requires for usualnormalizing treatment. It will be understood, however, that even thoughit is necessary to bring the drill blank to a suitably high temperaturebefore the operation illustrated in Fig. 6 is carried out, the surfaceportion of the lands which is displaced into the outer edges of thegrooves 40 will be densified or compacted in a manner similar to'thatoccurring when the operation is carried on cold. It may also be notedthat the line along which the metal is joined at the outer ends of thegrooves will be substantially imperceptible in the finished product andthat the entire surface portions. of the lands will be hard and smoothin the finished product so as not to engender packing of chips inoperation.

Although forming no part of the present invention, in Figs. 9, 10 and 11apparatus of a type suitable for carrying out the step of operationillustrated in Fig. 6 is shown. This apparatus is a machine including aflat base 50. At one end outer ends of which bear against the lower endsof the base 50 is a sub-base I extending centrally across which is anintegral upwardly extending wall 52 having triangularly shaped webs 58at its opposite ends extending between it and the sub-base 5I. A pair ofupwardly extending post members 54 are vertically adjustably secured tothe forward face of the wall 52, as viewed in Fig. 8, at opposite endsof the wall, by bolts 55 through slots 55 in the post members. The upperends of the members 54 are provided with aligned horizontal openings 51in each of which a plunger 58 is slidably received. The plungers 58 areeach of its corresponding roller 44 which is pivotally mounted thereonby means of a suitable pin- 68. 1 The posts 58 are so maintained by therespective collars 59 and pins 62 that the corresponding rollers 44 arearranged for contact with the drill blank passing between' them at anangle corresponding to the helix angle of the flutes in the drill blank.

A pair of supports I0, one fixed to, the wall 52 and the other directlyto the sub-base 5| respectively above and below the axes of the posts 58are provided with aligned openings 12 therein the axes of which may bearranged in intersecting relation with respect to the axes of theopenings 54 but which as shown are arranged slightly ofiset therefrom toinsure ample clearance between the rollers 44 and 42. Each of thesupports I0 threadably receive a post I4, the posts I4 extending towardsone another and having their adjacent ends coned and slotted as at I6for reception of the corresponding rollers 42 which are supportedthereon by means of pins I8. The

posts I4 are turned in their supports 10 so as to cause their respectiverollers 42 to be skewed an amount to correspond with the "spiral of theflutes 24 in the particular drill blank to be acted upon and they arelocked in this rotatably adjusted position by means of lock nuts 80 andset is provided. Each end of the wall 52 is provided with an outwardlyprojecting centrally slotted support 84, vertically offset from thecenters of the posts 58 and in which a lever 88 is pivotallymountedmidway between its endsby means of a pin 80. The upper end of each lever88 extends over the outer end of the corresponding post 58 and is thereprovided with an adjusting screw 90 adapted to bear against the outerend of the corresponding post 58 centrally thereof. The screws 82 may belocked in their adjusted posi- .tion by means of lock nuts 94. As willbe best observed from an inspection of Fig. 10 the levers 88 extenddownwardly at an angle and their lower ends lie outwardlyof'corresponding webs' 58 arranged at opposite ends of the sub-base 5|.Between the webs 88 a pair of spaced bosses 98, best shown,in'Fig.'9.are arranged on the sub-base 5| and aligned openings are provided in thewebs 1 58 bosses 88. In the thus aligned openings in each web 58 and itscorresponding boss 88 is axially slidably received a post or pin I00 theof the corresponding levers 88.

Rotatably supported upon a pin I02 between the bosses 88 in eccentricrelation with respect to the posts I00 is a cam member I 04. The cam Imember I04 is an axial type of cam, that is its peripheral portionswhich extend between the opposed ends of the posts I00 vary in thicknessin a circumferential direction. The cam I04 is provided with anoperating lever I06 which upon being operated to rotate the cam I04,will have the tendency to move the posts I00 outwardly where the cam I04is turned to bring a portion of increasing thickness between them. Thusit will be understood that if the cam I04 is turned by the handle I06 tobring a narrow portion of the cam between the opposed ends of the postI00,

screws 92 will move the posts 58 and consequently the rollers 44 towardeach other.

As indicated in Figs. 9 and 10, at the end of the base 50 opposite theapparatus thus described is secured a support IIO provided with anopening II2, preferably rectangular in section, disposed with its axisin the same horizontal plane as the axes of the posts 58 and with itsaxis in the same vertical plane as the axes of the posts N. A rack H4 isreciprocably received within the opening II2 andwithin the support I I0lies in mesh with a pinion I I6 secured to a shaft I I8 having bearingin the support H0 and receiving at its outer end a hand wheel I20. Aswill be apparent rotation of the hand wheel We acting through the shaftIE8 and gear H3- Will cause reciprocation of the rack H4 in the openingIE2.

The inner end of the rack H4 is provided with a suitable anti-frictionbearing 22, preferably of the combined radial and thrust type,,uponwhich is rotatably mounted a chuck I24 of a type suitable for receivingand holding the shank end of a drill blank with the axis of he drillblank in a horizontal plane including the axes of the posts 58 and in avertical plane including the axes of the posts I4.

With the apparatus thus described and assum-- ing that it is desired toemploy it to carry out the operation previously described in connectionwith Fig. 6, a drill blank of the stage of completion illustrated inFig. 5 is secured at its shank end within the chuck I24 at a time whenthe chuck I 24 has been moved to or adjacent the extreme limit of itsmovement in a direction to the right as viewed in Figs. 9 and 10. Thehandle I I06 of the cam I04 is then moved so as to permit the rollers 44to be separated from each other .a required amount to permit insertionof the drill blank between them. It may be assumed that the posts 14have previously beenadjusted so as to place the rollers 42 at an anglecorresponding to the flutes 24 of the drill blank and soas to be closelyreceived within such flutes and that theposts 58 have been previouslyadjusted to bring the rollers 44 at an "angle corresponding to the angleof the flutes 24 in the drill blank. The hand wheel I20 is then operatedtocause the outer end of the drill blank to be inserted bedesiredamount, and then the hand wheel I20 is turned to cause the drill blankto pass axially between the rollers 42 and 44, the rollers 42 actingthrough the flutes 24 to turn the blank about 5 its axis and the rollers44 acting upon'the lands of the drill blank to displace the metal in thepreviously described manner in a direction. tending to close the openends of the grooves 40. The drill blanks may be caused to pass back andforth between the rollers 42 and 44 any desired number of times requiredto obtain the full penetration of the rollers 44 into the drill blank,the cam I04 being turned at the end of each pass to obtain a furtherpenetration. In the smaller size of drill one or two passes at the mostmay be all that is required to obtain the desired penetration of therollers 44, the number of passes required usually increasing withincreased diameter of the drill.

It will be understood that the other operations required on the drillblank to bring it to its completed form may all be of a conventionalnature and, accordingly, do not require a showing of the apparatusdesigned to effect them.

It will be understood that the specific method of and apparatus forclosing the outer edges of the grooves 40 in the blanks described areillustrative of only one method among many which may be found suitablefor use'for carrying out this particular step of the present inventionand, accordingly, the present invention in its broader aspects is not tobe interpreted as being limited to this specific method and apparatus ofclosing the aforementioned grooves. be understood thatjormal changes maybe made in the specific steps and sequence of steps of operationdescribed, as well vas apparatus for carrying out such steps, withoutdeparting from the spirit or substance of the broad invention, the scopeof which is commensurate with the appended claims.

What I claim is:

1. In the formation of an oil hole drill, the step of forming agenerally cylindrical blank Patent NO. 25 148 ,8 5"

Accordingly, it will CERTIFICATE or CORRECTION.

STUART A. COGSDIIL. It is hereby certified that error appears fl n theprinted specification having a plurality of spirally arranged angularlyspaced flutes in the outer surface thereof and a correspondinglyspirally arranged groove in at least one of the lands between a pair ofsaid flutes, then working at least a portion of the surface layer'ofsaid land first in a generallycircumferential direction toward thecenter of said groove and then radially of said blank while the walls ofsaid groove are totally unsupported, said groove being of sufiicientdepth whereby the said working of said surface layer closes the openside of said groove without completely filling said groove, that portionof said surface thus worked being exclusive of the cutting edge of saidland whereby said portion of said land thus worked provides a relief forsaid drill behind said cutting edge.

2. In the manufacture of an oil hole twist drill including a metaldisplacing operation between rolls, the steps of operating upon acylindrically shaped metal blank to provide a plurality of spirallyarranged flutes therein, operating upon said blank to provide a groovein a land thereof between an adjacent pair of flutes and for a lengthcommensurate with. the length of said flutes, inserting said blankbetween said rolls, forcing said rolls radially inwardly against thesurface of the lands of said blank with at least one of said rolls inbridging relation with respect to said groove while the walls of saidgroove are totally unsupported, efiecting relative reciprocation betweensaid blank and said rolls axially of said blank and simultaneouslyguiding said blank for rotational movement about its axis throughcooperation with said flutes whereby to radially contract the dimensionof said blankv between said rolls and urge a portion of the metal actedupon by said rolls into the open edge of said groove'to close the same,said groove being of such depth that said rolling operation closes theopen edge thereof Without closing the bottom thereof.

STUART A. COGSDILL.

February as, .19 9.

of the above numbered patent requiring -'correction follower Page ifirst.

column, line 65, for the word "crown"read crowd; and second colunn',line 52, for "temperatures" read temperature; and'that the saidLettersPatent should be read with this correction therein" that the same may.conform the record of the case in the -P'atentoffice. v I I I Signed andsealed this 18th day of li r11, A.Ia.- 1959--.

(Seal) 'HenryVan Arsdale Acting commutator-er Patente-

